The goal of these studies is to determine the geometric and dynamic similarity criteria that characterize the mammalian circulatory system of all mammals, large and small, and to write mathematical equations describing the hemodynamics of the ventricles, aorta, arteries, capillaries, and veins. Plastic casts are being prepared of the arterial and venous systems in large and small mammals (horses, cows, goats, dogs, rabbits, rats) and measurements of the diameters and lengths of various arterial and venous segments are being made. These results are being analyzed from the standpoint of principle of similarity and indicate that the geometry of the mammalian vascular system can be described by certain power-law equations relating diameter and length of vessel segments to some power of body weight. Studies of the pressure-drop and velocity of flow in the ascending aorta are being carried out in large and small mammals and this data, in association with the geometrical data regarding the aorta, is being analyzed from the standpoint of the principle of similarity in an attempt to write mathematical equations describing the dynamics of flow in the ascending aorta.